1. Field of the Invention
The extensive use of the paper and mineral separation industries of cationic products as pigment retention aids capable of adjunctly serving as internal sizing agents or as flocculants has stimulated the introduction of a variety of cationic starches and flours resulting from the reaction of starchy materials with different organic nitrogen compounds. Several methods and reagents have been proposed in the last 20 years for preparation of cationic starches and flours.
2. Description of the Prior Art
Patents covering this field are well cited in review articles: Industrial Starches, Chemical Technology, Review No. 23, Ronald W. James, "Cationic Starches," pp. 98-140, Noyes Data Corporation, Park Ridge, N.J. (1974); Starch: Chemistry and Technology, Vol. 2, R. L. Whistler and E. F. Paschall, "Production and Uses of Cationic Starches," pp. 403-422, Academic Press, New York (1967); Starch and Its Derivatives, 4th Edition, J. A. Radley, "The Starch Esters and Ethers," pp. 385-419, Chapman and Hall Ltd., 11 New Fetter Lane, London EC4 (1968). Briefly, cationic starchy materials prepared with cation-bearing nitrogen reagents fall into two general categories. The first category includes those that are prepared in the presence of either small amounts of alkali or none at all using nitrogen reagents with alkylene epoxide groups as taught in U.S. Pat. Nos. 3,422,087, 3,448,101, 3,674,725; or using alkylene imines as taught in U.S. Pat. No. 3,522,238. The mechanism of this reaction is an addition etherification of the reagents with the starchy materials. The nature of this type of reaction precludes the formation of products having high cationic efficiencies. Generally, the efficiencies are in the range of 50-60%, thereby limiting the products' applications. The second category includes those that must be prepared in the presence of high amounts of alkali (3-15 weight percent starch basis, pH &gt;9) using nitrogen reagents with alkylene halides and/or alkylene epoxide groups as taught in U.S. Pat. Nos. 2,813,093, 2,876,217, 2,970,140, 3,346,563, 3,578,475, 3,666,751, 3,721,575, 3,737,370. The reaction mechanism for the alkylene halides is a substitution etherification with the starchy materials. Use of such high alkali concentrations and high pH's introduces a number of economical, ecological, energy-consuming, and end-use problems. The stability and utility of the products are greatly reduced unless they are neutralized and washed at the completion of the etherification to reduce their basicity and remove the neutral salts. This, of course, greatly increases the cost of the process, along with the original higher cost of using more alkali for the reaction. The neutralization and wash waters also create pollution problems. These factors all reduce the commercial desirability of the prior art methods of producing cationic starches.